Page 33 - Handbook of Adhesion Promoters

26 Mechanisms of Adhesion

46
polymerization. The twin polymerization was performed using the following monomers:
2,20-spirobi-[4H-1,3,2-benzodioxasiline] and 2-(3-amino-n-propyl)-2-methyl-4H-1,3,2-
46
benzodioxasiline. The resultant polymer is very convenient for use as an interphase
because it is produced without shrinkage and formation of low-molecular weight prod-
46
ucts.
Resist lithography is used in the electronics industry as a common microfabrication
47
technique. Epoxy oligomer (SU 8) is a favorite photoresist material but it suffers from
47
poor adhesion to silicon which is used as the common substrate. A layer of polyallylam-
ine was found to be an excellent adhesion promoter because it spontaneously absorbs on
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silicon and has amine groups reactive with epoxy oligomer. Figure 2.24 shows steps of
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microfabrication.
Figure 2.25 shows a method
of fabrication of a digital micro-
fluidic chip from poly(p-xylylene)
(Parylene C) and tantalum pentox-
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ide. Because both layers do not
have sufficient adhesion, the inter-
mediate layer has to be produced
48
to hold them together. This layer
is formed from γ-methacryloxy-
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propyltrimethoxy silane. During
the coating process, the surface of
Ta O reacts with adsorbed water
5
2
molecules in the air and forms a
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hydroxyl group, Ta−OH. The
hydroxyl group reacts with silane
forming a self-limited molecular
layer on the Ta O surface (Figure
2
5
48
2.25c). The monomers of
Parylene C deposited on the sur-
face of a polymerized silane (Fig-
ure 2.25b) copolymerize with the
methacryloxy tail via a free radical
addition reaction and deposit as a
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polymer layer. This technology
leads to the formation of very thin
(monomolecular) interface
48
enhancing adhesion.
Figure 2.26 shows the struc-
ture of electrode material com-
Figure 2.26. (a) Cross-sectional image of film without (3-glyci-
doxypropyl) trimethoxysilane prepolymer and (b) film with 1.0 posed of polyimide and copper
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wt% (3-glycidoxypropyl) trimethoxysilane prepolymer on polyim- paste. The copper paste is
o
ide substrate sintered at 275 C in nitrogen/HCOOH environment. applied on the surface of polyim-
[Adapted, by permission, from Jiang, J; Koo, YH; Kim, HW; Park,
JH; Kang, HS; Lee, BC; Kim, S-H; Song, H-e; Piao, L, Bull. ide core with 1 wt% of 3-glyci-
Korean Chem. Soc., 35, 10, 3025-9, 2014.] doxypropyltrimethoxysilane